Dispensing container



1966 H. HEISLER ETAL 3,229,865

DISPENSING CONTAINER Filed Oct. 25, 1964 2 Sheets-Sheet 1 01 v vovvmvwov wmvvmbw //Vl/E/V7'O/?$ HAROLD HE/SLER AL V/N M E/C OFF A] TTOR VEY 1966 H. HEISLER ETAL 3,229,855

DISPENSING CONTAINER Filed Oct. 23, 1964 2 Sheets-Sheet 2 //VVENTOR$ HAROLD HE/SLER flL V/N M (OFF ATTORNEY United States Patent 3,229,865 DISPENSING CONTAINER Harold Heisler, Rte. 3, Plainfield, Ill., and Alvin M. Eicoif, 155 E. Ohio St., Chicago, Ill. Filed Oct. 23, 1964, Ser. No. 406,021 Claims. (Cl. 222-391) The improved dispensing container comprising the present invention is designed for use primarily in Connection with the storage and dispensing of semiliquid substances, such as tooth paste, hair creme, ointment and similar toilet preparations of a viscous flowable nature. The invention is, however, capable of other uses and a dispensing container involving the principles of the invention, by suitable modifications if necessary, may be employed for the storage and dispensing of a wide variety of substances, whether the same be of a semiliquid or a liquid nature. Irrespective of the particular use to which the invention may be put, the essential features thereof are at all times preserved.

The present dispensing container is essentially a packaging container, which is to say that it lends itself admirably to the packaging industry in that it is susceptible of being filled by any standard or conventional filling apparatus or machine and, when so filled, it constitutes a scalable package type unit that is available for display and immediate use by the purchaser without preliminary manipulation or the use of tools or other utensils.

Many toilet cremes, such, for example, as tooth paste, hair preparations and similar semiliquid substances are currently packaged and marketed in flexible and collapsible squeeze-type containers which are commonly referred to as tubes. Such tubes are possessed of certain limitations including the susceptibility of such tubes to rupture after a period of use. When manual squeeze pressure is applied to a collapsible squeeze-type tube, it frequently happens that clogging at the dispensing orifice results in rupture or bursting of the tube at the remote end thereof. Additionally, the practice of progressively folding or rolling the rear end region of the tube occasionally cracks the tube along the folded corners so that the packaged material oozes from the cracks or seams thus created. Still further, the squeeze method of ejecting the contents of a tube seldom results in ejection of the entire contents of the tube in the last analysis and thus it represents a waste of material. Finally, a collapsible squeezer-type dispensing tube makes no provision for dispensing measured amounts of the material contained therein and the size or volume of the ejected dosages is invariably a function of uncertain manual pressure and of pressure duration.

The present invention is designed to overcome the above-noted limitations that are attendant upon the construction and use of conventional squeeze-type dispensing containers and, toward this end, the invention contemplates the provision of a novel dispensing container which closely resembles the conventional squeeze-type container; which employs as a storage housing for the material undergoing dispensing a rigid outer shell that is not collapsible and, therefore, is not subject to rupture, puncture or cracking due to the usual above-outlined causes that are associated with collapsible containers; which is capable of repetitively discharging measured quantities of the material undergoing dispensing; and which, moreover, is

ice

capable of completely emptying the container of its contents during the terminal dispensing operation to which it is subjected.

The provision of a dispensing container of the character briefly outlined above, and possessing the stated advantages constituting the principal object of the invention, a further object is to provide such a dispensing container wherein there is provided a novel manipulating means whereby, upon actuation thereof, a measured quantity of the packaged substance will be ejected from the container through the dispensing nozzle thereof and wherein the position which the manipulating means assumes with respect to the longitudinal axis of the container will serve as a visual indication of the quantity of the substance remaining in the container and yet to be dispensed.

The provision of a dispensing container which is of eX- tremely simple construction, consisting as it does of but three principal parts or assemblies and which, therefore, may be manufactured at a low cost; one which is comprised of a minimum number of moving parts and, there fore, is unlikely to get out of order; one which, in the main, is comprised of plastic components that readily lend themselves to conventional injection molding operations; one which is rugged and durable and, therefore, will withstand rough usage; one which is attractive in its appearance and pleasing in its design; and one which, otherwise, is well adapted to perform the services required of it, are further desirable features which have been borne in mind in the production and development of the present invention.

Other objects and advantages of the invention, not at this time enumerated, will readily suggest themselves as the nature of the invention is better understood.

In the accompanying two sheets of drawings forming a part of this specification, one illustrative and preferred embodiment of the invention is shown.

In these drawings:

FIG. 1 is a side elevational view of a dispensing container constructed according to the present invention, portions of the container shell being broken away in order more clearly to reveal the nature of the invention;

FIG. 2 is a front end view of the dispensing container;

FIG. 3 is a rear end view of the dispensing container;

FIG. 4 is a transverse sectional view taken on the line 4-4 of FIG. 1;

FIG. 5 is a transverse sectional view taken on the line 55 of FIG. 1;

FIG. 6 is an exploded side elevational view of the composite container shell devoid of contents;

FIG. 7 is a side elevational view, schematic in its representation and partly in section, illustrating the operation of the manipulating assembly that is employed in connection with the present invention, the assembly including a pusher element or piston for ejecting the contents of the container, a flexible thrust member for moving the pusher element, and a (graduated rack and pawl assembly for actuating the thrust member;

FIG. 8 is a front elevational view of the manipulating assembly that is shown in FIG. 7; and

FIG. 9 is an enlarged sectional view taken on the line 9-9 of FIG. 1.

Referring now to the drawings in detail and in particular to FIGS. 1 and 6, a dispensing container constructed according to the principles of the present invention is designated in its entirety by the reference numeral and it is comprised of three principal parts or assemblies including a tubular outer shell 12, a closure cap 14 for the rear end of the shell, and a shiftable inner composite material-displacement assembly 16 (see FIG. 7). The dispensing container 10 further includes a removable screwtype closure cap 18 at the front or dispensing end of the shell 12. The shell 12, the rear and front closure caps 14 and 18, and certain parts of the material-displacement assembly 16 are preferably formed of a suitable phenolic resin plastic material by injection molding processes, the particular material employed being of a rigid nature so that the assembly of the shell and the closure caps provides a rigid noncollapsible container for the semiliquid material or other substance underagoing dispensing.

The shell 12 is of tubular design and includes an elongated tubular body portion 20 which, in the exemplary form of the invention selected for illustration herein, is generally of elliptical cross section but which, if desired, may be constructed otherwise to have a circular or other cross sectional shape. At its front or dispensing end, the shell is provided with a frusto-conical portion 22, the slant angle of which is on the order of 45. Such conical portion terminates at its small base in a forwadly projecting dispensing nozzle 24 which is provided with external screw threads exteriorly threaded at 25 to receive thereover t-he screw-type closure cap 18.

As best seen in FIG. 5, the upper region of the tubular shell 12 is formed with a thickened Wall portion 26 and this thickened wall portion is provided with an elongated, longitudinally extending dovetail groove 27, the groove being formed with an upwardly facing convex arcuate bottom wall 28 (see also FIG. 9). As shown additionally in FIGS. 6 and 7, the bottom wall 28 is provided with a longitudinal series of teeth 29 therealong, the teeth, when considered collectively, establishing a longitudinally extending rack which is designed for cooperation with a certain spring biased pawl as will be described in greater detail presently.

The rear closure cap 14 is of elliptical cup-shape design and is conformable to the cross sectional shape of the body portion 20 of the shell 12. It includes a rear wall 30 and a continuous side wall 32. The forward rim 34 of the side wall 32 seats within a recess 36 (see FIG. 6) at the rear rim of the body portion 20 and the cap 14 may be permanently cemented or otherwise secured in position on the shell 12. As best seen in FIGS. 1 and 7, the rear wall 30 and the side wall 32 of the rear closure cap are formed with a thick web 38 which presents a forwardly facing concave arcuate reaction guide surface 39, the function of which will be made clear presently.

The material displacement assembly 16 is best seen in FIG. 7 and it is comprised of a displacement piston 40, a spring biased actuating pawl 42 therefor, and an interconnecting thrust member 44 in the form of a deformable flexible steel or other spring-biased tape.

The piston is longitudinally slidable within the shell 12 and is generally of frusto-conical design. The cross sectional shape of the piston is conformable to the cross sectional shape of the body portion 20 of the tubular shell 12. As shown in FIG. 1, the piston 40 includes an elliptical portion 46, one side of which is flattened as at 47 to accommodate the planar inside Wall surface 48 of the bottom wall 28 of the dovetail groove 27. A frusto-conical portion 49 extends forwardly from the elliptical portion 46, and a forwardly projecting tip 50 extends forwardly from the small base of the frusto-conical portion 49 and is designed for cooperation With a dispensing orifice 52 in the dispensing nozzle 24. The purpose of the tip 50 is to eject the last trace of the semifiuid material or substance from the container when the piston is in its extreme forward position within the shell 12. At the rear sidev of the piston 40, there is formed a rearwardly projecting rectangular boss 52 (see FIGS. 1, 4, 6 and 7) Within which is embedded or n hored One end of the flexible spring-biased tape constituting the thrust member 44.

The thrust member 44 is preferably in the form of a length of tape stock of the type commonly employed in the manufacture of carpenters steel measuring rules, the tape being formed of spring material such as stainless steel and being arcuate in cross sectional configuration. The arcuate cross sectional configuration of the tape lends a degree of stability to the tape when the latter is linearly straight but, when the tape is forcibly curved so that any given section thereof assumes a curvature having a radius less than a predetermined minimum, the thus curved section becomes linearly staright in transverse cross section.

As shown in FIGS. 1, 5, 8 and 9, the tape constituting the thrust member 44 is forcibly curved at a region designated at so that it provides a bight portion which fits snugly within the arcuate reaction guide surface 39. The upper reentrant portion of the tape is caused to overlie the toothed rack that is afforded by the teeth 29. The longitudinal side edges of this upper reentrant portion are confined and slidable in the opposed guide channels 62 (see FIG. 9) that are formed by reason of the dovetail groove 27 The lower reentrant portion of the tape underlies the thickened wall portion 26 of the shell 12 so that the piston 40 is longitudinally or axially slidable within the confines of the shell. The length of the tape .constituting thrust member 44 is slightly greater than the effective length of the body portion 20 of the shell and thus when the actuating pawl 42 assumes a position adjacent to the forward end of the shell, the piston will assume a position adjacent to the rear end of the shell, and. vice versa. The piston 40 and the actuating pawl 42 are movable in opposite directions and the position of either member is a function of the position of the other member. As the actuating pawl 42 is moved in either direction along the toothed rack afforded by the teeth 29, the tape will shift endwise and a transition from a condition of curved cross section to a condition of straight cross section will take place within the confines of the arcuate reaction guide surface 39, the piston40 being pushed or pulled,

as the case may be, in a direction opposite to the direc-.

tion of movement of the pawl 42.

Because of the fact that the side edges of the upper when the extreme forward edge 64 of the pawl is in engagement with a particular tooth 29, the pawl arches, over the next succeeding several teeth as shown in full lines in this view. When the medial region of the pawl 42 is depressed as shown in broken lines, the pawl is flattened out so that it bridges an additional tooth 29. Then, when pressure on the pawl is released, the pawl becomes re-- stored to its normal arcuate condition and the edge 64 thereof snaps over the next adjacent tooth 29 and the entire pawl becomes shifted rearwardly by a distance equal to the intertooth distance of the rack.

Upon initial depression of the pawl 42 as described above, the rear edge of the pawl is thus shifted rearwardly and the entire mass of the tape is shifted end-,

wise in a direction to thrust the piston 40 forwardly within the shell 12 a distance equal to such intertooth of the rack. Such forward movementof the piston displaces, a

commensurate amount of the semiliquid material or substance within the shell. Thus, a measured amount of the subsance is forced outwardly through the dispensing nozzle 24. The amount of the semiliquid substance which is. thus dis ensed at each pression of the actuati g P 5. 42 is equal to the internal cross sectional area of the shell multiplied by the intertooth distance of the rack.

In order to facilitate depression of the actuating pawl 42, as well as to lend a finished appearance to the dispensing device as a whole, and also to conceal and protect the pawl, a push button 70 is employed for actuating the pawl. This push button overlies the pawl, rests lightly upon the crest portion of the pawl, and is confined in a box-like structure 72 of plastic material. The box-like structure includes a top wall 74 having an Opening 76 therethrough for projection of the push button 70. The structure 72 also includes depending sides having outturned lower edges 78 (see FIG. 9) which slide in the opposed guide channels 62. The box-like structure 72 is suitably secured to the tape constituting the thrust member 44 in any suitable manner, for example, by suitable adhesive such as an epoxy resin or the like.

It is contemplated that the dispensing container 10 of the present invention shall be marketed as a disposable item originally filled with the desired semiliquid substance which may, for example, be tooth paste or the like. A newly purchased item will thus be in such condition that the actuating pawl 42, together with its associated enclosing box-like structure 72 and operating push button 70 will assume a position adjacent to the front end of the shell 12, while the piston 40 will assume a position adjacent to the rear end of the shell. As the contents of the shell are dispensed by the ejection of measured quantities thereof in the manner previously outlined, the position of the push button along the rack afforded by the teeth 29 will serve as an indication of the quantity of the semiliquid substance remaining within the shell.

From the above description, it is believed that the nature of the illustrated dispensing container 10, as well as its operation, will be readily apparent. The invention is not to be limited to the precise arrangement of parts shown in the accompanying drawings or described in this specification as various changes in the details of construction may be resorted to without departing from the spirit or scope of the invention. For example, whereas the container 10 is adapted for use as a disposable item of merchandise as described above, it is contemplated that, if desired, the same by suitable modification be employed as a refillable container adapted to contain semiliquid substance as a lubricating grease, a prepared semiliquid foodstuff such as lard or the like, or a medicinal preparation. In such an instance, the container shell may be formed of stainless steel or the like and the rear closure cap 14 may be removable from the rear of the shell 12 for refilling purposes. Additionally, the character of the dispensing nozzle 24 and of its dispensing orifice 52 may be varied to effect different flow patterns of the semiliquid substance undergoing ejection from the shell. Therefore, only insofar as the invention has particularly been pointed out in the accompanying claims is the same to be limited.

Having thus described the invention what we claim as new and desire to secure by Letters 'Patent is:

1. In a dispensing container, in combination, a tubular shell adapted to contain a quantity of semiliquid material,

means at the forward end of the shell defining a dispensing orifice, a rear wall closing the rear end of the tubular shell, a piston disposed within said shell and slidable axially therein from a rear retracted position wherein it assumes a position adjacent to the rear end of the shell and a forward advanced position wherein it assumes a position adjacent to the forward end of the shell, means on the upper outer surface of said shell defining a toothed rack which extends longitudinally of the shell from a region adjacent to the forward end thereof to a region adjacent to the rear end thereof, a flexible resilient thrust tape having one end thereof secured to the piston and the other end thereof overlying said rack, said tape being reversed upon itself in a medial region thereof to provide an upper linearly straight reentrant portion which overlies the rack, a lower linearly straight reentrant portion which is substantially coaxial with the shell and a curved interconnecting bight portion, said bight portion engaging said rear wall and being slidable thereon as the tape is shifted endwise during movement of the piston forwardly within the shell, and an actuating pawl on the forward end of the upper reentrant portion, engageable with said toothed rack, and operable upon repeated depression and release thereof to shift said upper reentrant portion progressively rearwardly along the rack and thus effect progressive forward step-by-step movement of the piston in a forward direction within the shell to eject measured quantities of the material from the shell through said dispensing orifice.

-2. In a dispensing container, the combination set forth in claim 1 and wherein said thrust tape is formed of spring material and is normally arcuate in transverse section whereby the reentrant portions of the tape are yieldingly maintained linearly straight.

6. In a dispensing container, in combination, a tubular shell adapted to contain a quantity of semiliquid material, means at the forward end of the shell defining a dispensing orifice, a. rear wall closing the rear end of the tubular shell, a piston disposed within said shell and slidable axially therein from a rear retracted position wherein it assumes a position adjacent to the rear end of the shell and a forward advanced position wherein it assumes a position adjacent to the forward end of the shell, means on the upper outer surface of said shell defining a toothed rack which extends longitudinally of the shell from a region adjacent to the forward end thereof to a region adjacent to the rear end thereof, a flexible resilient thrust tape having one end thereof secured to the piston and the other end thereof overlying said rack, said tape being reversed upon itself in a medial region thereof to provide an upper linearly straight reentrant portion which overlies the rack, a lower linearly straight reentrant portion which is substantially coaxial with the shell and a curved interconnecting bight portion, said bight portion engaging said rear wall and being slidable thereon as the tape is shifted endwise during movement of the piston forwardly within the shell, a limited forward end region of said upper reentrant portion of the thrust tape being arcuate in transverse cross section and being bowed upwardly whereby said end region constitutes a manipulating pawl, the forward edge of said end region being engageable with successive teeth on said rack upon depression and release of said end region.

4. In a dispensing container, the combination set forth 'in claim 3 and wherein said thrust tape is formed of spring material and is normally arcuate in transverse section whereby the reentrant portions of the tape are yieldrngly maintained linearly straight.

5. In a dispensing container, in combination, a tubular shell adapted to contain a quantity of semi-liquid material, means at the forward end of the shell defining a dispensing orifice, a rear wall closing the rear end of the tubular shell, a piston disposed within said shell ands lidable axially therein from a rear retracted position wherem it assumes a position adjacent to the rear end of the shell and a forward advanced position wherein it assumes a position adjacent to the forward end of the shell, means on the upper outer surface of said shell defining a toothed rack which extends longitudinally of the shell from a region adjacent to the forward end thereof to a region adjacent to the rear end thereof, a flexible resilient thrust tape having one end thereof secured to the piston and the other end thereof overlying said rack, said tape being reversed upon itself in a medial region thereof to provide an upper linearly straight reentrant portion which overlies the rack, a lower linearly straight reentrant portion which is substantially coaxial with the shell and a curved interconnecting bight portion, said bight portion engaging said rear wall and being slidable thereon as the tape is shifted endwise during movement of the piston forwardly within the shell, means defining a pair of opposed guideways on opposite sides of said rack, the longitudinal side edges of said upper reentrant portion being slidably disposed within said guideways, and an actuating pawl on the forward end of the upper reentrant portion, engageable .with said toothed rack, and operable upon repeated depression and release thereof to shift said upper reentrant portion progressively rearwardly along the rack and thus effect progressive forward stepby-step movement of the piston in a forward direction within the shell to eject measured quantities of the material from the shell through said dispensing orifice.

6. In a dispensing container, in combination, a tubular shell adapted to contain a quantity of semiliquid material, means at the forward end of the shell defining a dispensing orifice, a rear wall closing the rear end of the tubular shell, a piston disposed within said shell and slidable axially therein from a rear retracted position wherein it assumes a position adjacent to the rear end of the shell and a forward advanced position wherein it assumes a position adjacent to the forward end of the shell, the upper portion of the wall of said shell being thickened, said thickened portion being formed with an upwardly facing elongated dovetail groove therein, the sides of which define a pair of opposed guideways, the bottom Wall of said groove being provided with a series of longitudinally extending teeth thereon which, collectively, define an elongated longitudinally extending rack, a flexible resilient thrust tape having one end thereof secured to the piston and the other end thereof overlying said rack, said tape being reversed upon itself in a medial region thereof to provide an upper linearly straight reentrant portion which overlies the rack disposed within said dovetail groove and overlies the rack, a lower linearly straight reentrant portion which is substantially coaxial with the shell and a curved interconnecting bight portion, said bight portion engaging said rear wall and being slidable thereon as the tape is shifted endwise during movement of the piston forwardly within the shell, the longitudinal side edges of the upper reentrant portion of the tape being confined between and slidable in said guideways, and an actuating pawl on the forward end of the upper reentrant portion, engageable with said toothed rack, and operable upon repeated depression and release thereof to shift said upper reentrant portion progressively rearwardly along the rack and thus effect progressive forward step-by-step movement of the piston in a forward direction within the shell to eject measured quantities of the material from the shell through said dispensing orifice.

7. In a dispensing container, the combination set forth in claim 6 and wherein said manipulating pawl on the forward end of the upper reentrant portion of the thrust tape is integral with the tape and comprises an upwardly bowed portion at the extreme forward end of said upper reentrant portion and the forward edge of which is engageable with said rack.

8. In a dispensing container, in combination, a tubular shell adapted to contain a quantity of semiliquid material, means at the forward end of the shell defining a dispensing orifice, a rear wall closing the rear end of the tubular shell, a piston disposed within said shell and slidable axially therein from a rear retracted position wherein it assumes a position adjacent to the rear end of the shell and a forward advanced position wherein it assumes a position adjacent to the forward end of the shell, means on the upper outer surface of said shell defining a toothed rack which extends longitudinally of the shell from a region adjacent to the forward end thereof to a region adjacent to the rear end thereof, a flexible resilient thrust tape having one end thereof secured to the piston and the other end thereof overlying said rack, said tape being reversed upon itself in a medial region thereof to provide an upper linearly straight reentrant portion which overlies the rack, a lower linearly straight reentrant portion which is substantially coaxial with the shell and a curved interconnecting bight portion, said rear wall of the shell being formed with a forwardly facing curved reaction surface, said bight portion of the thrust tape engaging said reaction surface and I being slidable thereon as the tape is shifted endwise during movement of the piston forwardly within the shell, and an actuating pawl on the forward end of the upper reenr 9. In a dispensing container, in combination, a tubular shell adapted to contain a quantity of semiliquid material, means at the forward end of the shell defining a dispensing orifice, a rear wall closing the rear end of the tubular shell,

a piston disposed within said shell and slidable axially therein from a rear retracted position wherein it assumes a position adjacent to the rear end of the shell and a forward advanced position wherein it assumes a position adjacent to the forward end of the shell, means on the upper outer surface of said shell defining a toothed rack which extends longitudinally of the shell from a region adjacent to the forward end thereof to a region adjacent to the rear end thereof, a flexible resilientthrust tape having one end thereof secured to the piston and the other end thereof overlying said rack, said tape being reversed upon itself in a medial region thereof to provide an upper linearly straight reentrant portion which overlies the rack, a lower linearly straight reentrant portion which is substantially coaxial with the shell and a curved interconnecting bight portion, said bight portion engaging said rear wall and,

being slidable thereon as the tape is shifted endwise during movement of the piston forwardly within the shell, an actuating pawl on the forward end of the upper reentrant portion, engageable with said toothed rack, and operable upon repeated depression and release thereof to shift said upper reentrant portion progressively rearwardly along the rack and thus effect progressive forward step-by-step;

movement of the piston in a forward direction within the shell to eject measured quantities of the material from the shell through said dispensing orifice, a depressible push button overlying said pawl and operable upon depression thereof to actuate the pawl, and a housing for said push button and within which the latter is slidable, said housing being secured to and movable bodily with the forward end region of the thrust tape. t

10. In a dispensing container, in combination, a tubular shell adapted to contain a quantity of semiliquid material, means at the forward end of the shell defining a dispensing orifice, a rear wall closing the rear end of the tubular shell, a piston disposed within said shelland slidable axially therein from a rear retracted position wherein it assumes a position adjacent to the rear'end of the shell and a forward advanced position wherein it assumes a position adjacent to the forward end of the shell, the upper portion of the wall of said shell being thickened, said thickened portion being formed with an upwardly facing elongated dovetail groove therein, the sides of which define a pair of opposed guideways, the bottom wall of said groove being provided with a series of longitudinally extending teeth thereon which, collectively, define an elongated longitudinally extending rack, a flexible resilient thrust tape having one end thereof secured to the piston and the reentrant portion of the tape being confined between and slidable in said guideways, and an actuating pawl on the forward end of the upper reentrant portion, engageable with said toothed rack, and operable upon repeated depression and release thereof to shift said upper reentrant portion progressively rearwardly along the rack and thus effect progressive forward step-by-step movement of the piston in a forward direction within the shell to eject measured quantities of the material from the shell through said dispensing orifice, a depressible push button overlying said pawl and operable upon depression thereof to References Cited by the Examiner UNITED STATES PATENTS 2,127,794 8/1938 Wastman 1S555 2,240,046 4/ 1941 Marta 222-391 LOUIS I. DEMBO, Primary Examiner. 

1. IN A DISPENSING CONTAINER, IN COMBINATION, A TUBULAR SHELL ADAPTED TO CONTAIN A QUANTITY OF SEMILIQUID MATERIAL, MEANS AT THE FORWARD END OF THE SHELL DEFINING A DISPENSING ORIFICE, A REAR WALL CLOSING THE REAR END OF THE TUBULAR SHELL, A PISTON DISPOSED WITHIN SAID SHELL AND SLIDABLE AXIALLY THEREIN FROM A REAR RETRACTED POSITION WHEREIN IT ASSUMES A POSITION ADJACENT TO THE REAR EAND OF THE SHELL AND A FORWARD ADVANCED POSITION WHEREIN IT ASSUMES A POSITION ADJACENT TO THE FORWARD END OF THE SHELL, MEANS ON THE UPPER OUTER SURFACE OF SAID SHELL DEFINING A TOOTHED RACK WHICH EXTENDS LONGITUDINALLY OF THE SHELL FROM A REGION ADJACENT TO THE FORWARD END THEREOF TO A REGION ADJACENT TO THE REAR END THEREOF, A FLEXIBLE RESILIENT THRUST TAPE HAVING ONE END THEREOF SECURED TO THE PISTON AND THE OTHER END THEREOF OVERLYING SAID RACK, SAID TAPE BEING REVERSED UPONE ITSELF IN A MEDIAL REGION THEREOF TO PROVIDE AN UPPER LINEARLY STRAIGHT REENTRANT PORTION WHICH OVER- 